Such a valve, which includes a closing unit applied against a seat by a compression spring is described in particular in French Pat. No. 1 021 221.
However, to adjust the valve to match local working conditions, the valve must include a setting device for the compression spring. Now, adjusting such a device is a particularly long and tricky process. Indeed, firstly, valve protection hoods must be removed for access to the adjustment device and secondly, after the spring has been set, the elimination of the tangential component of the force due to the spring entails suitable adjustment of its antagonistic bearing collar disposed at the end distant from the closing unit.
Other known valves, e.g. U.S. Pat. No. 2,243,711 (Lamb), include hydraulic control by piston jacks. Friction of the seals of such pistons against the walls of the cylinders is liable to impair mechanical blocking and sealing.
The invention aims to provide a particularly simple over-pressure release valve for which adjustment requires no dismantling and which operates without said friction.